The diol 1,4:3,6-dianhydro-D-sorbitol, also referred to herein as isosorbide, has the formula shown by Khanarian et al. in U.S. Pat. No. 5,958,581 at column 1, line 55. Isosorbide is readily made from renewable resources, such as sugars and starches. For example, isosorbide can be made from D-glucose by hydrogenation followed by acid-catalyzed dehydration. Poly(1,3-propylene-co-1,4:3,6-dianhydro-D-sorbitol terephthalate) is referred to as 3GIT and poly(1,3-propylene terephthalate) as 3GT. Di-1,3-propylene glycol is referred to as DPG. 1,3-propylene glycol is also referred to as 1,3-propanediol or “3G”. Trademarks are shown in upper case.
The relatively low glass transition temperature (Tg) of 3GT (˜45–50° C.) can lead to slight tackiness of the polymer when stored at high temperatures. An instance of this is sometimes evidenced on spools of fiber stored in warehouses in hot weather.
Charbonneau et al., in U.S. Pat. No. 6,063,464, disclose the preparation of copolymers prepared from isosorbide, one or more other diols, and a diacid or diester such as terephthalic acid or its dimethyl ester. The diols include 1,3-propanediol. Claimed uses of such polymers include resins, films, sheets, beverage bottles, fibers, optical articles, etc. An example of the preparation of 3GIT was provided, with the ratio 1,3-propanediol:isosorbide being 22:1 as charged. The measured content of isosorbide in the resulting polymer was 0.3 mole %. In spite of discussing the increased Tg resulting from the inclusion of isosorbide in other poly(alkylene diol-co-isosorbide terephthalate)s, the Tg for this example decreased.
It is desirable to prepare 3GITs with a low level of color and a Tg higher than the 45–50° C. Tg of 3GT, and, most importantly, both a low level of color and a higher Tg. Such improved properties aid in the use of 3GIT in many markets, including beverage bottles, film or sheet, fibers, monofilaments, and optical articles (e.g., compact disc or digital versatile disc). In many of these markets, aesthetics are important, and having a very low color resin is highly desirable.